Recently, a new class of thermoelastic sulfonated polymers has been described in a number of U.S. patents. These sulfonated polymers are derived from polymeric materials having olefinic unsaturation, especially elastomeric polymers such as Butyl and EPDM rubbers. U.S. Pat. No. 3,642,728, herein incorporated by reference, clearly teaches a method of selective sulfonation of olefinic unsaturation sites of an elastomeric polymer to form an acid form of a sulfonated elastomeric polymer. The olefinic sites of the elastomeric polymer are sulfonated by means of a complex of a sulfur trioxide donor and a Lewis base. The SO.sub.3 H groups of the sulfonated elastomer can be readily neutralized with a basic material to form an ionically cross-linked elastomer having substantially improved physical properties over an unsulfonated elastomer at room temperature. However, these ionically cross-linked elastomers may be processed like a conventional thermoplastic at elevated temperatures under a shear force in the presence of selected preferential plasticizers which dissipate the ionic associations at the elevated temperatures thereby creating a reprocessable elastomer.
The basic materials used as neutralizing agents are selected from organic amines or basic materials selected from Groups I, II, III, IV, V, VIB, VIIB and VIII and mixtures thereof of the Periodic Table of Elements. Although these sulfonated elastomeric polymers prepared by the process of this patent are readily usable in a certain number of limited applications, they are not as readily adaptable for the manufacture of an injection moldable elastomeric article such as footwear as are the improved compositions of the present invention, wherein both improved physical and rheological properties are realized. Although U.S. Pat. No. 3,642,728 refers generally to the blending of sulfonated EPDM terpolymers with unsulfonated elastomers, it does not contemplate or envision the use of a Kraton rubber in conjunction with a polypropylene thermoplastic resin.
U.S. Pat. No. 3,836,511, herein incorporated by reference, teaches an improved process for the sulfonation of the olefinic sites of the elastomeric polymer, wherein the improved sulfonating agent is selected from acetyl sulfate, propionyl sulfate and butyryl sulfate. The neutralizing agents employed to neutralize the acid form of the sulfonated elastomeric polymers are organic amines. The resultant ionically cross-linked sulfonated elastomers prepared by this process do not exhibit both the improved physical and rheological properties of the compositions of the present invention.
U.S. Pat. No. 3,870,841, herein incorporated by reference, teaches a method of plasticization of the polymeric backbone of a neutralized sulfonated plastic polymer by means of a polymer chain plasticizer which is a liquid compound having a boiling point of at least about 120.degree. F. The polymer chain plasticizer is selected from a dialkyl phthalate, a process oil or an organic acid ester. Additionally, a domain plasticizer can be incorporated into the composition, wherein the domain plasticizer reversibly disrupts the association of the sulfonate groups at a temperature of forming. The compositions formed by this process are not as suitable for the manufacture of high performance elastomeric articles such as footwear formed by an injection molding process as are the compositions of the present invention.
U.S. Pat. No. 3,847,854, herein incorporated by reference, teaches a method of improving the processability of neutralized sulfonated elastomeric polymers by the addition of a preferential plasticizer which has at least one functional constituent which exhibits a bond moment whose absolute value is at least 0.6 Debyes, and must be a liquid at the desired processing temperature of the neutralized sulfonated elastomeric polymer. Again, the compositions of the present invention are more adaptable for use in the manufacture of high performance elastomeric articles.
Products resulting for the aforementioned methods for obtaining neutralized sulfonated elastomeric compositions, possess either unsuitable rheological or physical properties for the applications envisioned in the present invention.
For example, the physical properties of these resultant sulfonated elastomeric products of these aforementioned patents are unsuitable for a major application of an injection molding process, namely the manufacture of footwear, wherein excellent resilience, dimensional stability, excellent low and high temperature flexibility, excellent flex fatigue, and excellent abrasion are needed. Furthermore, the high melt viscosity and melt elasticity of these materials makes injection molding difficult if not impossible. These materials of the aforementioned patents which are generally processable by only compression molding, have unsuitable physical properties for this major application of footwear.
U.S. Pat. Nos. 3,974,240 and 3,974,241 describe the blending of a crystalline polyolefinic material with a neutralized sulfonated elastomeric polymer in an attempt to improve both the rheological and physical properties of the elastomeric polymer. The selection of the use of the crystalline polyolefinic material to improve both the stiffness as well as improving the melt viscosity of the composition was based in part upon the limitation of the use of fillers such as carbon black, clays, calcium carbonate or silicates as a single additive to the elastomeric polymer. Although fillers in combination with an elastomeric polymer increase the hardness of the composition, these fillers deteriorate the melt viscosity of the resultant composition. These material are more adaptable for stiff elastomeric articles such as rubberized chair tips or wheels whereas the compositions of the present invention are more adapted for flexible elastomeric articles such as elastomeric footwear due to the blend of the Kraton, polypropylene thermoplastic resin and the sulfonated EPDM terpolymer.
The unique and novel improved compositions of the present invention overcome the deficiencies of the aforementioned U.S. Patents from both a rheological and physical properties aspect. The blend compositions of the present invention solve the problem of having a material which has both desirable rheological and physical properties for the manufacture of an elastomeric article as an elastomeric footwear, wherein the extrudate of the resultant compositions do not exhibit melt fracture during extrusion processing as in the case in some of the aforementioned patents.